As is known in the art, glass sheets may be curved by a curving mold comprising a series of curved or arched steel rods which extend parallel to each other transversely of the direction of glass travel. Typically, these rods are rotatable in unison about an axis passing through their two ends and their inclination determines the radius of curvature imparted to the glass sheet. Each curved rod is surrounded by a tubular sleeve made of stainless steel which possesses substantial torsional strength but is flexible in the axial direction. The sleeve is rotatably mounted on the curved rod and fixed at one end to a pinion so as to permit rotation regardless of the inclined position of the curved rod.
To minimize friction, the inside diameter of the tubular sleeves is made larger than the diameter of the curved rods and the sleeves are supported on graphite bearing rings disposed at spaced intervals along the length of each curved rod. Each ring is capable of rotating about the rod. Such an arrangement is disclosed in U.S. Pat. No. 3,831,239 to Hoff et al.
In such prior art devices, the curved rods of the curving section are situated in the open air. In this way the curved rods and the rings are air cooled and their temperature remains relatively low.
For ordinary glass the temperature at the inlet of the tempering section should be on the order of 600.degree. to 650.degree. C., and it should generally not be less than 610.degree. C. Since the glass temperature drops about 70.degree. C. during such a curving operation in the open air, the glass must be heated in the oven an additional 70.degree. C. to a temperature between 670.degree. and 720.degree. C., depending on the type of glass. This elevated temperature results in certain disadvantages. For example, defects in the glass become evident, particularly the undulations whose pitch depends on the geometry of the roller bed which conveys the glass to the oven. Another obvious drawback is the large energy consumption required to attain the elevated temperature.